Method of preparing polymer using allyl-and xylyl-amine containing initiators

ABSTRACT

An anionic polymerization initiator includes the C-lithio reaction product of an organolithium compound and a tertiary-amino allyllithium or a tertiary-amino xylyllithium. When used in an anionic polymerization, a functional group from the initiator is incorporated onto the head of the growing polymer and a lithium atom is incorporated at the &#34;living&#34; end of the polymer chain prior to quenching. The initiator may be used to polymerize a monomer(s) including diolefin monomers, monovinyl aromatic monomers and trienes, and the living ends of the polymers are effectively maintained even at temperatures of up to 300° F. and higher. Such polymers exhibit an increased efficiency in coupling termination reactions, and products prepared from such polymers exhibit improved hysteresis characteristics. Products such as tires and the like can be prepared from such polymers and from vulcanizable elastomer compositions employing the polymers.

This application is a division of application Ser. No. 08/363,111, filedDec. 23, 1994.

TECHNICAL FIELD

The subject invention relates to the anionic polymerization of dienepolymer and copolymer elastomers. More particularly, the presentinvention relates to anionic polymerization employing anamine-containing initiator compound. The amine initiator is atertiary-amino allyllithium or a tertiary-amino xylyllithium.

Diene polymers and copolymers prepared according to the presentinvention, have reduced hysteresis characteristics. Articles such astires, power belts and the like prepared from these polymers exhibitincreased rebound, decreased rolling resistance and less heat build-upduring mechanical stress operations. Further, the present initiatorsallow polymerizations to be run at high temperatures which is useful,for example, in promoting subsequent termination reactions such ascoupling, or additions of hysteresis-reducing terminal groups.

BACKGROUND OF THE INVENTION

In the art it is desirable to produce elastomeric compounds exhibitingreduced hysteresis. Such elastomers, when compounded to form articlessuch as tires, power belts and the like, will show an increase inrebound, a decreased rolling resistance and less heat build-up whenmechanical stresses are applied.

Previous attempts at preparing reduced hysteresis compounds haveincluded high temperature mixing of the filler-rubber mixtures in thepresence of selectively-reactive promoters to promote compoundingmaterial reinforcement; surface oxidation of the compounding materials;chemical modifications to the terminal end of polymers usingtetramethyldiaminobenzophenone (Michler's ketone), tin coupling agentsand the like and, surface grafting thereon. All of these approaches havefocused upon increased interaction between the elastomer and thecompounding materials.

It has also been recognized that carbon black, employed as a reinforcingfiller in rubber compounds, should be well dispersed throughout therubber in order to improve various physical properties. One example ofthe recognition is provided in published European Pat. Appln. EP 0 316255 A2 which discloses a process for end capping polydienes by reactinga metal terminated polydiene with a capping agent such as a halogenatednitrile, a heterocyclic aromatic nitrogen-containing compound or analkyl benzoate. Additionally, the application discloses that both endsof the polydiene chains can be capped with polar groups by utilizingfunctionalized initiators, such as lithium amides.

The present invention provides novel initiators for anionicpolymerization, to form elastomers with functional groups derived fromsaid initiators. The functional groups are incorporated into the polymerchain providing improved dispersability of carbon black throughout theelastomeric composition during compounding. As will be describedhereinbelow, these initiators are compounds containing a moiety derivedfrom a tertiary-amino allyllithium or a tertiary-amino xylyllithium.

Organolithium polymerization initiators are also known in the art. Forexample, U.S. Pat. No. 3,326,881 discloses phenyllithium initiator andU.S. Pat. No. 3,439,049 discloses an organolithium initiator preparedfrom a halophenol in a hydrocarbon medium. Phenyllithium initiators haveproven to be unstable.

U.S. Pat. No. 4,015,061 is directed toward amino-functional initiatorswhich polymerize diene monomers to form mono- or di-primary arylamine-terminated diene polymers upon acid hydrolysis.

U.S. Pat. No. 4,914,147 discloses terminal modifying agents includingdialkylamino-substituted aromatic vinyl compounds such asN,N'-dimethylamino benzophenone and p-dimethylamino styrene, in rubbercompositions having reduced hysteresis characteristics. In U.S. Pat. No.4,894,409, an amino group-containing monomer, such as2-N,N-dimethylaminostyrene is polymerized to form an aminogroup-containing diene based polymer.

It is also known in the art to conduct polymerizations employinghydrocarbon lithium initiators at high temperatures. However, elevatedtemperatures make it more difficult to maintain the "living" ends or thepolymerlithium bonds needed for efficient polymerization and terminationreactions. With known initiators it has been found that the lithiumconstituent will often combine with an available alpha-hydrogen atom,resulting in lithium hydride, especially at elevated temperatures,thereby destroying the initiator and causing additional harmful sidereactions. Hence, high temperature polymerizations have proven to bedifficult to maintain and difficult to terminate efficiently.

A need exists therefore, for a polymerization initiator which whenemployed in an anionic polymerization, will result in a polymer chainhaving a functional group derived from the initiator. A need also existsfor such an initiator which will perform effectively at hightemperatures resulting in narrow molecular weight distribution polymersand retention of "living" ends.

SUMMARY OF INVENTION

It is therefore an object of the present invention to provide anionicpolymerization initiators which promote the incorporation of functional,active groups in the polymer chain.

It is another object of the present invention to provide a method ofpreparing an anionic polymerization initiator.

It is another object of the present invention to provide afunctionalized polymer.

It is still another object of the present invention to provide a methodfor the preparation of a functionalized polymer and for thepolymerization of the polymer at high temperatures.

At least one or more of the foregoing objects together with theadvantages thereof over the existing art, which shall become apparentfrom the specification which follows, are accomplished by the inventionas hereinafter described and claimed.

In general an anionic polymerization initiator of the present inventioncomprises the metalation product of an organo lithium compound and atertiary-amino compound having a general formula selected from ##STR1##where R₁ and R₂ are the same or different and are selected from alkyls,cycloalkyls and aralkyls having from about 1 to about 12 carbon atoms;R₃ is a group selected from allyl, 2-methallyl and xylyl; R₄ is acarbocyclic group of from about 3 to about 20 methylene groups; each R₅is an alkyl having from about 1 to about 20 carbon atoms; and x is aninteger of from about 0 to about 10.

There is also provided a method of preparing an anionic polymerizationinitiator, which comprises reacting an organo lithium compound with atertiary-amino compound having a general formula selected from ##STR2##where R₁, R₂, R₃, R₄, R₅ and x are as described hereinabove.

A polymer according to the invention comprises a polymer chain havingthe general formula R₆ -polymer-Li prior to quenching; wherein R₆ is afunctional group derived from a polymerization initiator having ageneral formula selected from ##STR3## where R₁, R₂, R₄, R₅ and x are asdescribed hereinabove and R'₃ is formed by removing a hydrogen atom fromthe aforedescribed R₃ group.

A method according to the invention for preparing a polymer comprisesinitiating polymerization of at least one monomer selected from diolefinmonomers having from about 4 to about 12 carbon atoms, monovinylaromatic monomers having from about 8 to about 20 carbon atoms, andtrienes, in the presence of a polymerization initiator having a generalformula selected from ##STR4## wherein R₁, R₂, R'₃, R₄, R₅ and x are asdescribed hereinabove.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

As will become apparent from the description which follows, the presentinvention provides a novel lithio amine initiator for anionicpolymerization of diene homopolymer and copolymer elastomers. Polymermolecules prepared with these initiators contain a functional group, andit has been discovered herein that vulcanizable elastomeric compoundsand articles thereof made from such functionalized polymer moleculesexhibit useful properties, particularly, reduced hysteresis. Whencompounded to make products such as tires, power belts and the like,these polymeric products of this invention exhibit increased rebound,decreased rolling resistance and less heat build-up during periods ofapplied mechanical stress.

It has been further unexpectedly found that polymerizations employinginitiators according to the invention can be conducted at elevatedtemperatures as high as the peak temperatures resulting from theexothermic polymerization reactions, such as from about 120° F. to about300° F. (about 49° C. to about 149° C.), or even higher temperatures. Itis theorized that because the invention initiators either have noalpha-hydrogens proximate the lithium atom, or because thealpha-hydrogens are bonded to a carbon atom having a double bond, suchas when the alpha hydrogen is bonded to a vinyl carbon, there is areduced tendency for the lithium constituent of the initiator to beeliminated as lithium hydride. Furthermore, the lithium amidefunctionality, which is a likely promoter of side reactions, is absentin the present initiators. Hence, the living ends of the polymers areeffectively maintained even at high temperatures. It is to beappreciated that polymerizations conducted at such elevated temperaturesresult in more efficient polymerizations and improved terminationreactions, including improved monomer randomization and improvedcoupling ability of the polymers.

The initiators according to the present invention are amine-containingcompounds. More particularly, the initiators according to the presentinvention are C-lithio allyl- or xylyl-amines having one or the other ofthe following general formulas: ##STR5## where R₁ and R₂ are the same ordifferent and can be, for example, alkyls having from 1 to about 12carbon atoms, cycloalkyls having from 3 to about 14 carbon atoms, andaralkyls having from 6 to about 20 carbon atoms. R'₃ is derived byremoval of a hydrogen atom from an allyl, 2-methallyl, or a xylyl group,and R₄ contains from about 3 to about 20 methylene groups to form acyclic amine group. The cyclic amines are preferred, and further, of thexylyl amines, ortho-xylyls are preferred. Such ortho-xylyl amines can bedepicted as: ##STR6## The methylene groups in R₄ can be substituted withpreferably an alkyl R₅, having from about 1 to about 20 carbon atoms.Either none, a part or all of the methylenes in R₄ may be substituted,and hence, "x" is an integer of from 0 to about 20. When x is 0, all themethylenes are --CH₂ -- groups; when x is 1, one of the methylenes is a--CHR₄ or the like. Examples of initiators with substituted R₄methylenes include ##STR7## (where R₄ is a pentamethylene and x is 3)##STR8## (where R₄ is pentamethylene and x is 1) and the like.

The initiators according to the present invention are preferably themetalation reaction product of an organolithium compound and an allyl-or xylyl-amine compound. One preferred class of organolithium compoundshas the general formula RLi, where R is selected from the groupconsisting of alkyls and cycloalkyls having from about 1 to about 20carbon atoms. Typical alkyls include n-butyl, s-butyl, methyl, ethyl,isopropyl and the like. The cycloalkyls include cyclohexyl, menthyl andthe like. It has been found, that at least certain of the metalatedinitiators according to the invention, are more stable than lithiumamide initiators as will be demonstrated hereinbelow.

As stated above, the organolithium compound is reacted with a an allyl,2-methallyl or xylyl-amine compound, such as one of those having thefollowing general structure: ##STR9## where R₁, R₂, R₃, R₄, R₅ and x areas defined hereinabove. The metalation reaction forming the initiatorsof this invention can, thus, be depicted as: ##STR10## wherein R₃ is anallyl (--CH₂ CH--CH₂), ##STR11## or xylyl (--CH₂ PhCH₃) group, or thelike; R, R₁, R₂, R₃ and R'₃ are as described hereinabove; and Ph is aphenyl group.

Examples of useful initiators include hexamethyleneimino-o-xylyllithium(HMI--XyLi), pyrrolidino-o-xylyllithium(Py--XyLi),piperidino-o-xylyllithium(Pip--XyLi),hexamethyleneimino-methallyllithium (HMI--MAILi),hexamethyleneiminoallyllithium (HMI--AILi) andN,N-dioctylamino-allyllithium (DOA--MAILi).

The initiator according to the present invention can be prepared byforming a solution of the allyl- or xylyl-amine compound in ananhydrous, aprotic solvent, such as cyclohexane or hexane. To thissolution is then added the organolithium compound (R i) in the same or asimilar solvent. Both are allowed to react for approximately one to 24hours at ambient temperature (25° C. to 30° C,). The metalation processis facilitated by additions of small amounts of an aprotic polar solventsuch as an ether such as tetrahydrofuran (THF) in an amount of about 1to about 40 mM THF per mM Li, with about 2-10 mM of THF being preferred.Amounts of the two reactants range from about 1.0 moles of the aminecompound to about 1.0 to about 1.4 moles of organolithium compound, witha slight excess (5-10 molar percent) of organolithium being preferred.It is to be appreciated by one skilled in the art that various reactiontemperatures and times may be useful and are within the scope of thepresent invention. Furthermore, other polar aprotic solvents such astertiary amines and various other ethers may be added to give a solublecatalyst and enhanced metalation.

The initiator thus prepared, is employed to polymerize anyanionically-polymerizable monomer to yield a polymer elastomer.Typically the initiator is used to polymerize unsaturated hydrocarbonmonomers such as butadiene, isoprene and the like, and copolymersthereof with monovinyl aromatics such as styrene, alpha methyl styreneand the like, or trienes such as myrcene. Thus, the elastomers includediene homopolymers from monomer A and copolymers thereof with monovinylaromatic monomers B. Exemplary diene homopolymers are those preparedfrom diolefin monomers having from 4 to about 12 carbon atoms. Exemplaryvinyl aromatic copolymers are those prepared from monomers having from 8to about 20 carbon atoms. Preferred elastomers include dienehomopolymers such as polybutadiene and polyisoprene and copolymers suchas styrene butadiene rubber (SBR). Copolymers can comprise from about 99to 20 percent by weight of diene units and from about 1 to about 80percent by weight of monovinyl aromatic or triene units, totalling 100percent. The polymers and copolymers of the present invention may have1,2-microstructure contents ranging from about 10 to about 80 percent,with the preferred polymers or copolymers having 1,2-microstructurecontents of from about 25 to 65 percent, based upon the diene content.

The copolymers are preferably random copolymers which result fromsimultaneous copolymerization of the monomers A and B as is known in theart. The block copolymers, poly(b--B--b--A--b--B), result from theseparate polymerization of the monomers forming the A and B polymers asis known in the art. Often, such block copolymers which includepoly(b-styrene-b-butadiene-b-styrene) are thermoplastic elastomers,sometimes referred to as S--B--S polymers.

The initiators of the present invention form "living polymers" from theforegoing monomers, the general formula of which prior to quenching is

    R.sub.6 --polymer--Li

where the polymer is any of the foregoing diene homopolymers, monovinylaromatic homopolymers, diene/monovinyl aromatic random copolymers andblock copolymers and R₆ is a functional group derived from theinitiator. Thus, the polymers of this invention, R₆ -polymer Li, canalso be represented by the following formulas: ##STR12## where polymer,R₁, R₂, R₄, R₅ and x are as defined hereinabove and Li is a lithium atombonded to a carbon atom. The lithium proceeds to move down the growingchain polymer, as polymerization continues, until the reaction isquenched.

Polymerization is usually conducted in a conventional solvent foranionic polymerizations such as hexane, cyclohexane, benzene and thelike. Other techniques for polymerization, such as semi-batch andcontinuous polymerization may be employed. In order to promoterandomization in copolymerization and to increase vinyl content, a polarcoordinator may optionally be added to the polymerization ingredients.Amounts range between 0 to 90 or more equivalents per equivalent oflithium. The amount depends upon the type of polar coordinator that isemployed, the amount of vinyl desired, the level of styrene employed andthe temperature of the polymerizations, as well as the selectedinitiator.

Compounds useful as polar coordinators are organic and includetetrahydrofuran, linear and cyclic oligomeric oxolanyl alkanes such as2-2'-di(tetrahydrofuryl)propane, 2,2-bis(tetrahydrofuryl)propane,di-piperidyl ethane, hexamethylphosphoramide, N-N'-dimethylpiperazine,diazabicyclooctane, dimethyl ether, diethyl ether, tributylamine and thelike. The linear and cyclic oligomeric oxolanyl alkane polarcoordinators are described in U.S. Pat. No. 4,429,091 the subject matterof which regarding polar coordinators is incorporated herein byreference. Other compounds useful as polar coordinators include thosehaving an oxygen or nitrogen hetero-atom and a non-bonded pair ofelectrons. Examples include dialkyl ethers of mono and oligo alkyleneglycols; "crown∞ ethers; tertiary amines such as tetramethylethylenediamine (TMEDA).

Polymerization is begun by charging a blend of the monomer(s) andsolvent to a suitable reaction vessel, followed by the addition of thepolar coordinator and the initiator solution previously described. Theprocedure is carried out under anhydrous, anaerobic conditions. Often,it is conducted under a dry, inert gas atmosphere. The polymerizationcan be carried out at any convenient temperature such as 32° F. (0° C.)to 300° F. (149° C.). For semi-batch polymerizations, temperatures of atleast about 180° F. (82° C.) are preferred. For batch polymerizations,it is preferred to maintain the peak temperature at from about 120° F.to about 300° F. (about 49° C. to about 149° C.), and more preferablyfrom about 180° F. to about 250° F. (about 82° C. to about 121° C.).Polymerization is allowed to continue under agitation for about 0.15 to24 hours. After polymerization is complete, the product is terminated inone or more ways.

For example, a protic quenching agent may be employed to give amonofunctional polymer chain. Quenching may be conducted in water, steamor an alcohol such as isopropanol, or any other suitable method.Quenching may also be conducted with a functional terminating agent,resulting in a difunctional polymer. Compounds providing terminalfunctionality (e.g., "endcapping") can be used such as tintetrachloride, (R₇)₃ SnCl, (R₇)₂ Sncl₂, R₇ SnCl₃, carbodiimides,N-cyclic amides, N,N' disubstituted cyclic ureas, cyclic amides, cyclicureas, isocyanates, Schiff bases, 4,4'-bis(diethylamino) benzophenone,and the like. Tin tetrachloride is preferred. The organic moiety R₇ isselected from the group consisting of alkyls having from about 1 toabout 20 carbon atoms, cycloalkyls having from about 3 to about 20carbon atoms, aryls having from about 6 to about 20 carbon atoms andaralkyls having from about 7 to about 20 carbon atoms. Typical alkylsinclude n-butyl, s-butyl, methyl, ethyl, isopropyl and the like. Thecycloalkyls include cyclohexyl, menthyl and the like. The aryl andaralkyl groups include phenyl, benzyl and the like. Preferred endcappingagents are selected from the group consisting of tin tetrachloride,tributyl tin chloride, dibutyl tin dichloride and1,3-dimethyl-2-imidazolidinone.

While terminating to provide a functional group on the terminal end ofthe polymer is preferred, it is further preferred to terminate by acoupling reaction, with for example, tin tetrachloride or other couplingagent such as silicon tetrachloride (SiCl₄), esters and the like. Asstated above, it has been found that the invention initiators providefor polymers having living ends maintained thereon. This allowseffective and efficient tin coupling using tin tetrachloride, whichresults in a polymer having improved processability and resistance tohot and cold flow. It is preferred that the polymers according to thepresent invention have at least about 40 percent tin coupling. That is,about 40 percent of the polymer mass after coupling is of highermolecular weight than the polymer before coupling as measured, forexample, by gel permeation chromotography. DOA--MAILi(N,N-dioctylaminomethallyllithium), while effective for initiatingpolymerizations resulting in an elastomers exhibiting reducedhysteresis, also results in terminated polymers having only about 30percent tin coupling, and hence, is not as preferred as the othersinitiators, as will be shown hereinbelow.

The terminating agent is added to the reaction vessel, and the vessel isagitated for about 1 to about 1000 minutes. Further examples ofterminating agents include the terminators described in U.S. Pat. No.5,066,729, the subject matter of which regarding terminating agents isincorporated by reference herein. It is to be understood that practiceof the present invention is not limited solely to these terminatorsinasmuch as other compounds that are reactive with the polymer boundcarbon-lithium moiety can be selected to provide a desired functionalgroup.

Quenching is usually conducted by stirring the polymer and quenchingagent for about 0.05 to about 2 hours at temperatures of from about 30°C. to 120° C. to ensure complete reaction. Polymers terminated with afunctional group as discussed hereinabove, are subsequently quenchedwith alcohol or other quenching agent as also described hereinabove.

Lastly, the solvent is removed from the polymer by conventionaltechniques such as drum drying, extruder drying, vacuum drying or thelike, which may be combined with coagulation with water, alcohol orsteam. If coagulation with water or steam is used, oven drying may bedesirable.

The polymers of the present invention contain a functional group at thehead of the polymer chain (derived from the initiator) in addition to anoptional functionality at the terminal end of the chain (derived fromthe terminating agent). These functional groups have an affinity forcompounding materials such as silica or carbon black. Such compoundingresults in products exhibiting reduced hysteresis, which means a producthaving increased rebound, decreased rolling resistance and lessened heatbuild-up when subjected to mechanical stress. Products including tires,power belts and the like are contemplated. Decreased rolling resistanceis, of course, a useful property for pneumatic tires, both radial aswell as bias ply types and thus, the vulcanizable elastomericcompositions of the present invention can be utilized to formtreadstocks for such tires. The composition can also be used to formother elastomeric tire components such as subtreads, black sidewalls,body ply skims, bead fillers and the like.

Polymers prepared according to the present invention and terminated orcoupled with tin tetrachloride, show reduced hysteresis and increasedcoupling as compared to polymers initiated with conventional initiatorssuch as n-butyllithium, as will be more fully explored hereinbelow.

The polymers of the present invention can be utilized as 100 parts ofthe rubber in the treadstock compound or, they can be blended with anyconventionally employed treadstock rubber which includes natural rubber,synthetic rubber and blends thereof. When the polymers of the presentinvention are blended with conventional rubbers, the amounts can varywidely with a lower limit comprising about 10 to 20 percent by weight ofthe total rubber. It is to be appreciated that the minimum amount willdepend primarily upon the degree of hysteresis reduction desired. Thus,the compounds can contain 10-100% by weight of the inventive polymer,with the balance, if any, being a conventional rubber.

The polymers can be compounded with all forms of carbon black in amountsranging from about 5 to 80 parts by weight, per 100 parts of rubber(phr), with about 35 to 60 phr being preferred. The carbon blacks mayinclude any of the commonly available, commercially-produced carbonblacks but those having a surface area (EMSA) of at least 20 m² /gramand more preferably at least 35 m² /gram up to 200 m² /gram or higherare preferred. Surface area values used in this application are thosedetermined by ASTM test D-1765 using the cetyltrimethyl-ammonium bromide(CTAB) technique. Among the useful carbon blacks are furnace black,channel blacks and lamp blacks. More specifically, examples of thecarbon blacks include super abrasion furnace (SAF) blacks, high abrasionfurnace (HAF) blacks, fast extrusion furnace (FEF) blacks, fine furnace(FF) blacks, intermediate super abrasion furnace (ISAF) blacks,semi-reinforcing furnace (SRF) blacks, medium processing channel blacks,hard processing channel blacks and conducting channel blacks. Othercarbon blacks which may be utilized include acetylene blacks. Mixturesof two or more of the above blacks can be used in preparing the carbonblack-containing compositions of the invention. Typical values forsurface areas of usable carbon blacks are summarized in the TABLE Ihereinbelow.

                  TABLE I    ______________________________________    CARBON BLACKS    ASTM           Surface Area    Designation    (m.sup.2 /g)    (D-1765-82a)   (D-3765)    ______________________________________    N-110          126    N-220          111    N-339          95    N-330          83    N-550          42    N-660          35    ______________________________________

The carbon blacks utilized in the preparation of the rubber compounds ofthe invention may be in pelletized form or an unpelletized flocculentmass. Preferably, for more uniform mixing, unpelletized carbon black ispreferred.

The reinforced rubber compounds can be cured in a conventional mannerwith known vulcanizing agents at about 0.1 to 10 phr. For a generaldisclosure of suitable vulcanizing agents one can refer to Kirk-Othmer,Encyclopedia of Chemical Technology, 3rd ed., Wiley Interscience, N.Y.1982, Vol. 20, pp. 365-468, particularly "Vulcanization Agents andAuxiliary Materials" pp. 390-402. Vulcanizing agents can be used aloneor in combination.

Vulcanizable elastomeric compositions of the invention can be preparedby compounding or mixing the functionalized polymers herein with carbonblack and other conventional rubber additives including for example,fillers, such as silica, plasticizers, antioxidants, curing agents andthe like using standard rubber mixing equipment and procedures. Suchelastomeric compositions when vulcanized using conventional rubbervulcanization conditions have reduced hysteresis properties and areparticularly adapted for use as tread rubbers for tires having reducedrolling resistance.

GENERAL EXPERIMENTAL

In order to demonstrate the preparation and properties of elastomersprepared according to the present invention, a number of initiators wereprepared. The initiators were then used to polymerize a solution ofbutadiene/styrene monomers. For comparison, polymerizations employingbutyllithium and lithium amide initiators were also carried out.

TABLE II provides a listing of abbreviations, compound names andstructures as used in the following examples and tables.

                                      TABLE II    __________________________________________________________________________    Abbreviations/Compounds/Structures    ABBREVIATION              COMPOUND     STRUCTURE    __________________________________________________________________________    BuLi      n-butyllithium                           CH.sub.3 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 Li    HMILi     lithium hexamethyleneimide                            ##STR13##    PyLi      lithium pyrrolidinide                            ##STR14##    HMIXyLi   hexamethyleneimino-o- xylyllithium                            ##STR15##    PyXyLi    pyrrolidino-o-xylyllithium                            ##STR16##    PipXyLi   piperidino-o-xylyllithium                            ##STR17##    HMIMAlLi  hexamethyleneimino- methallyllithium                            ##STR18##    HMIAlLi   hexamethyleneimino- allyllithium                            ##STR19##    DOAMAlLi  N,N-dioctylamino- methallyllithium                            ##STR20##    __________________________________________________________________________

1. HMI--XyLi Initiator

In order to prepare HMI--XyLi, 60.8 grams ofN-orthoxylylhexamethyleneimine, 60 milliliters (ml) of drytetrahydrofuran (THF) and 240 ml of dry hexane were added to a 28 ouncebeverage bottle with a magnetic stirrer. The bottle was capped with arubber liner and a crown two-hole cap. The bottle was then purged withnitrogen and placed on a magnetic stirrer plate. One hundred andninety-six ml of a 1.68 molar solution of n-butyllithium (n--BuLi) inhexane, was added dropwise via a syringe to the stirred solution ofN-orthoxylylhexamethyleneimine at room temperature, and stirringcontinued overnight.

In order to determine the amount of conversion, a small sample of thereaction mixture was reacted with ClSiMe₃ (where Me is methyl) in THF.The reaction product was analyzed by gas chromatography, which showed anabsence of BuSiMe₃. This indicated that all of the n--BuLi has reacted.Gilman titrations of additional samples of the reaction mixture showedthat 89.6 percent of the lithium present was in the form of C--Li bonds.

2. Polymer Preparation Using HMI--XyLi

A 28 ounce beverage bottle was washed and then dried in an oven at 145°C., capped with a rubber liner/2 hole crown cap, and purged withnitrogen until room temperature was reached. To the bottle was added236.8 grams of a blend of 75 percent by weight of 1,3-butadiene and 25percent by weight of styrene in hexane. The two monomers comprised 20percent by weight of the blend with hexane. To promote randomization,0.26 millimoles (mM) of 2,2-bis (tetrahydrofuryl) propane in hexane (0.5molar) was added. To this was then added 0.474 mM of HMI--XyLi preparedas hereinabove.

The beverage bottle was tumbled in an 80° C. water bath for 45 minutes,following which 0.38 ml of a 0.25 molar solution of tin tetrachloride inhexane was added. The bottle was then tumbled in a 50° C. water bath for1 hour, after which the bottle was cooled to room temperature. There wasthen added to the viscous cement in the bottle, 1 cubic centimeter (cc)of isopropanol and 4 cc of a di-t-butyl-p-cresol (DBPC) solution (11.0grams of DBPC in 700 cc hexane). The DBPC solution served as anantioxidant to prevent degradation of the polymer. The polymer wasisolated by coagulation in 1100 cc of isopropanol followed by vacuumoven drying at 50°-55° C.

The polymer showed a glass transition temperature (Tg) at -34° C. and anMn of 164,390, and a percent coupling of 61 percent (by gel permeationchromatography, G.P.C., analysis).

3. Large Scale Polymer Preparation

A. Batch Polymerization

Larger quantities of polymer were prepared under N₂ pressure in a 2gallon, closed, stainless steel reactor vessel. The reactor allowed fortemperature control and monitoring.

An "initial charge" preparation of a styrene/butadiene rubber (SBR) wasmade with the reactor temperature set at 122° F. (50° C.). A 75 weightpercent butadiene and 25 weight percent styrene blend in hexane (19percent by weight of monomers) was added to the reactor, followed byHMI--XyLi at 0.9 millimoles per 100 grams of monomer. The batchtemperature peaked at 197° F. Five minutes after this temperature wasreached, tin tetrachloride was added and the mixture was stirred for 30minutes while the temperature was allowed to fall. The polymer wasplaced into isopropanol containing an antioxidant.

B. Semi-Batch Polymerization

In a semi-batch polymerization, the butadiene/styrene monomers weremetered into the reactor at 200° F. (93.3° C.). This allowed for randomdistribution of the styrene monomer. It was found that with N--Liinitiators such as hexamethyleneimine-lithium (HMI--Li), poorconversions to polymer and very little tin tetrachloride coupling wouldresult. In contrast, with the HMI--XyLi initiator of this invention,high conversions to polymer (greater than 95 percent) and acceptablecoupling (51-55 percent) were realized.

4. Polymer Evaluations

TABLE III below shows percent couplings of SBR polymers made with therecited initiators and terminated with tin tetrachloride. The table alsoshows the hysteresis loss, tan delta, of the polymers compounded in thestandard test formula as provided in TABLE IV. All of the polymers inTABLE III were prepared at 80° C. in a manner similar to the methodsdescribed hereinabove. The desired target properties of the polymersprepared included an improvement, i.e., a reduction in the tan deltavalues over the control n--BuLi initiated polymers while stillmaintaining high levels, preferably greater than 40 percent, ofcoupling. In TABLE III, zero percent coupling indicates a polymer whichwas not reacted with tin tetrachloride, but rather was terminated withisopropanol. Also, where ranges are given the results are from more thanone sample.

                  TABLE III    ______________________________________    Tan Delta and % SnCl.sub.4 Coupling for SBR's (20-25% styrene)    Prepared at 80° C.    Initiator   Percent Coupling                             Tan. Delta (50° C.)    ______________________________________    BuLi.sup.a  56-64        0.116-0.124    BuLi.sup.a  0            0.183    PyLi.sup.a  17-20        0.094-0.102    HMI-Li.sup.a                22-34        0.102    HMI-Li.sup.a                0            0.103    HMI-XyLi    47-63        0.096-0.108    HMI-XyLi    0            0.117-0.138    Py-XyLi     55           0.103    Py-XyLi     0            0.147    Pip-XyLi    47           0.109    Pip-XyLi    0            0.150    HMI-MAlLi   48-57        0.105-0.106    HMI-MAlLI   0            0.147    HMI-AlLi    35-52        0.109-0.123    HMI-AlLi    0            0.104-0.118    DOA-MAlLi   30           0.138    DOA-MAlLi   0            0.157    ______________________________________     .sup.a Comparative, i.e., noninvention examples

                  TABLE IV    ______________________________________    Compounding Test Formulation    COMPONENT     PARTS BY WEIGHT    ______________________________________    Polymer       100    Black (N-351) 55    Naphthenic Oil                  10    Zinc Oxide    3    Antioxidant   1    Wax           2    Stearic Acid  2    Sulfur        1.5    Accelerator   1    ______________________________________

High levels of coupling are desirable in order to maintain goodprocessability in the subsequent manufacturing of rubber products.Further, it is known that when polymers are compounded as for example,in the formulation shown in TABLE IV, compound viscosities are increasedsignificantly. To attain manageable compound viscosities, lowermolecular weight polymers must be used. However, these lower molecularweights result in both cold and hot flow problems during manufacturingprocesses and polymer storage. A known remedy for these problems is totin couple the living anionic polymers using for example, tintetrachloride. It has been found according to the present invention,that high couplings of 40 percent or higher are achieved.

From the data reported in TABLE III, it is shown that the N--Li orlithium amide type initiators (HMI--Li and PyLi) give polymers havingreduced tan delta as compared to n--BuLi initiated polymers. However,these same polymers give unacceptably low levels of tin tetrachloridecoupling. The initiators according to the present invention, includingHMI--XyLi, PyXyLi, Pip--XyLi, HMI--MAILi and HMI--AILi, gave both lowtan deltas and high levels of tin tetrachloride coupling.

TABLE V shows stress/strain data for vulcanizates made from the testformulation of TABLE IV. Samples were cured for 20 minutes at 165° C.All of the SBR polymers were random copolymers, i.e., styrenedistribution was random or non-block, with 20-25 percent by weight ofstyrene. Regardless of styrene content, the polymers were all targetedfor glass transition temperatures of -40° C., within 5 degrees. Thus thelower styrene polymers generally contained higher levels of 1,2microstructure in the butadiene portion of the polymers. Examples ofmicrostructure variations versus Tg are given in TABLE VI. Themicrostructures were determined by NMR analysis which also confirmed therandom styrene distribution.

                  TABLE V    ______________________________________    Stress/Strain for SBR's Made at 80° C. with    Various Initiators/SnCl.sub.4 - Coupling                        Tensile    Elong. @ Break    Initiator             300%M, psi Strength, psi                                   Percentage    ______________________________________    Py-Li.sup.a             2189       2210       353    Py-Li.sup.a             2315       2728       388    HMI-Li.sup.a             2792       3144       377    HMI-Li.sup.a             2452       3023       405    HMI-XyLi 2520       3279       416    HMI-XyLi 2365       3107       369    Py-XyLi  2471       2471       345    Pip-XyLi 2338       2796       401    HMI-MAlLi             2691       3073       371    HMI-AlLi 2357       2846       400    DOA-MalLi             2111       2679       415    ______________________________________     .sup.a Comparative, i.e., noninvention examples

                  TABLE VI    ______________________________________    Microstructure - Tg Relationship                        Percentage                                  Percentage 1,2 Bd    Initiator Tg, °C.                        Styrene   (Bd = 100)    ______________________________________    HMI-Li.sup.a              -45       26.3      43.0    HMI-Li.sup.a              -38       20.4      53.1    HMI-Li.sup.a              -39.5     26.4      47.4    HMI-XyLi  -32       26.4      54.4    ______________________________________     .sup.a Comparative, i.e., noninvention examples

Ranges of molecular weights and molecular weight distributions (Mw/Mn)together with respective Tg data, are shown in TABLE VII. Molecularweights of 110,000 for the non-coupled polymers were expected from theamounts of monomers and initiators charged.

                  TABLE VII    ______________________________________    Molecular Weight Data for Polymers Made at 80° C.                              Percentage Coupling    Initiator             Mn      Mw/Mn    (SnCl.sub.4).sup.b                                           Tg, °C.    ______________________________________    PyLi.sup.a             138,046 1.80     20           -37    HMI-Li.sup.a             133,862 1.60     26           -41    HMI-Li.sup.a             105,364 1.26      0           -37    HMI-XyLi 206,545 2.02     54           -38    HMI-XyLi 119,120 1.16      0           -40    HMI-XyLi 164,386 1.86     61           -34    HMI-MAlLi             196,217 2.38     48           -33    Py-XyLi  175,465 1.78     55           -33    Py-XyLi  106,711 1.20      0           -36    Pip-XyLi 228,512 1.91     47           -35    Pip-XyLi 147,814 1.20      0           -42    HMI-AlLi 127,464 1.89     35           -38    HMI-AlLi 110,280 1.22      0           -37    ______________________________________     .sup.a Comparative, i.e., noninvention examples     .sup.b "0" coupling indicates terminations with isopropanol instead of     SnCl.sub.4 -

In batch polymerizations, the polymerizations were allowed to exotherm,resulting in a peak temperature of about 180° F. to about 300° F. (about82° C. to about 149° C.). As the concentration of monomers wasincreased, the peak temperatures also increased. Normally, ifundesirable results at high temperatures are encountered, the monomerconcentration must be decreased, resulting in reduced productivity. Theeffects of peak temperature increases on tin tetrachloride coupling withN--Li initiators are shown in TABLE VIII.

                  TABLE VIII    ______________________________________    Temperature Effects on % Coupling Via SnCl.sub.4    In Initial Charge Reactor Polymerizations             Peak      Percentage    Initiator             Temp., °F.                       Coupling   Polymer    ______________________________________    HMI-Li.sup.a             140       74         SBR    HMI-Li.sup.a             194       58         SBR    HMI-Li.sup.a             202       59         SBR    HMI-XyLi 197       93         SBR    HMI-Li.sup.a             228       26         BR (low 1,2 content)    HMI-XyLi 228       67         BR (low 1,2 content)    ______________________________________     .sup.a Comparative, i.e., noninvention examples

The percent coupling is significantly reduced as peak temperature isincreased in polymerizations with HMI--Li initiators. In thepolybutadiene (BR) example, a fairly high peak temperature was observedbecause of the higher starting temperature necessary in polymerizationswith no or very little vinyl modifier (e.g., ethers or trialkyl amines).With the HMI--XyLi invention initiator, improved level of coupling athigh temperatures is observed.

In the semi-batch 5BR polymerizations, the monomers are charged at hightemperatures, preferably about 200° F. to about 250° F. (about 93° C. toabout 121° C.), which forces random distribution of styrene in thecopolymer. With N--Li type initiators such as HMI--Li, there is lowconversion to polymer and poor tin tetrachloride coupling. TABLE IXshows results obtained from semi-batch preparation of SBR usingHMI--XyLi at 202° F. to 205° F. (94.4° C. to 96.1° C.), with tintetrachloride coupling.

                  TABLE IX    ______________________________________    Semi-Batch Preparation of SBR Using HMI-XyLi    Batch Percent   Percent  Percent       50° C. Tan    T, °F.          Conversion                    Coupling Styrene Tg, °C.                                           Delta    ______________________________________    205   98.5      55       34.2    -42   0.103    202   97.5      51       38.5    -35   0.111    ______________________________________

The data shows high conversion to SBR with desirable tan deltas andsufficiently high percent coupling to prevent subsequent flow problems.The polymers had a molecular weight before coupling of from 115,800 to121,700.

As stated above, other terminators can also be employed in the practiceof the present invention. For example, 1,3-dimethyl-2-imidazolidinoneand 1-methyl-2-pyrrolidinone were employed and resulted in SBR polymerswith Mn of 74,127 and 91,129 respectively, and when compounded, tandeltas of 0.102 and 0.107 respectively.

In conclusion, it is clear from the foregoing examples and specificationdisclosure that the initiators of the present invention are useful forthe anionic polymerization of diene monomers at elevated temperatures,to form homopolymers as well as copolymers with monovinyl aromaticpolymers or trienes. The resulting elastomeric polymers have afunctional group at the site of initiation and a lithium atom at theterminal, "living" end. After quenching, the polymers still retain thefunctional group at the site of initiation, which promotes uniform andhomogeneous mixing with carbon black. As a result vulcanizableelastomeric compounds containing these polymers exhibit improvedhysteresis which provides lower rolling resistance in tires and improvedfuel economy. Additionally, the lithium terminated polymers can bequenched with compounds to provide terminal functional groups and hence,difunctional polymer chains. The polymers also exhibit improved tintetrachloride coupling.

it is to be understood that the invention is not limited to the specificreactants, initiators, and organolithium compounds disclosed nor to anyparticular modifier or solvent. Similarly, the examples have beenprovided merely to demonstrate practice of the subject invention and donot constitute limitations of the invention. Those skilled in the artmay readily select other monomers and process conditions, according tothe disclosure made hereinabove.

Thus, it is believed that any of the variables disclosed herein canreadily be determined and controlled without departing from the scope ofthe invention herein disclosed and described. Moreover, the scope of theinvention shall include all modifications and variations that fallwithin the scope of the attached claims.

What is claimed is:
 1. A method of preparing a polymer comprising:polymerizing at least one monomer selected from diolefin monomers havingfrom about 4 to about 12 carbon atoms, monovinyl aromatic monomershaving from about 8 to about 20 carbon atoms, and trienes, in thepresence of a polymerization initiator having a general formula selectedfrom ##STR21## wherein R₁ and R₂ are the same or different and areselected from alkyls, cycloalkyls and aralkyls having from 1 to about 12carbon atoms; R'₃ is a group selected from allyl, 2-methallyl and xylyl,with one hydrogen atom removed; R₄ is a carbocyclic group of from about3 to about 20 methylene groups; each R₅ is an alkyl substituent on amethylene group having from 1 to about 20 carbon atoms; and, x is aninteger of from 0 to about
 10. 2. A method, as set forth in claim 1,comprising the further step of terminating said polymerization with aterminating or coupling agent.
 3. A method, as set forth in claim 2,wherein said terminating agent is selected from SnCl₄, R₇(3) SnCl, R₇(2)SnCl₂, R₇ SnCl₃, carbodiimides, N-cyclic amides, N,N' disubstitutedcyclic ureas, cyclic amides, cyclic ureas, isocyanates, Schiff bases,and 4,4'-bis(diethylamino) benzophenone, where R₇ is selected fromalkyls having from about 1 to about 20 carbon atoms, cycloalkyls havingfrom about 3 to about 20 carbon atoms, aryls having from about 6 toabout 20 carbon atoms and aralkyls having from about 7 to about 20carbon atoms.